In optical transmitters and transceivers, a laser diode driver circuit generates electrical drive signals that are used to drive a laser diode. The laser diode driver circuit and the laser diode are typically formed in separate integrated circuits (ICs). In particular, the laser diode driver circuit is typically formed in a transmitter (Tx) IC and the laser diode is typically formed in a laser diode IC. The ICs are typically mounted on a printed circuit board (PCB) or a flex circuit and electrically interconnected by electrically-conductive traces of the PCB or flex circuit.
It is known in optical Tx and transceiver technology to include active peaking circuitry in the Tx IC for performing peaking of the electrical drive signals generated by the laser diode driver circuitry. Active peaking circuitry in the Tx IC typically comprises a pre-distortion or pre-equalization circuit, such as a feed forward equalizer (FFE), for example, that shapes the electrical drive signal before it is input to the laser diode. Such pre-distortion or pre-equalization circuits emphasize or de-emphasize the amplitude of the electrical drive signal. The pre-distortion or pre-equalization process is often referred to as “laser peaking.” In general, laser peaking involves using a pulse to add or subtract current from the rising and/or falling edge of the electrical drive signal. The goal is to balance the rise/fall times of the electrical drive signal to improve the eye opening of the optical signal produced by the laser diode.
While active peaking circuitry currently used in many Tx ICs generally works well at achieving this goal, it increases the cost of the Tx IC due to the additional die area that the circuitry consumes and the increased complexity of the IC design. In addition, the active components (e.g., amplifiers) of active peaking circuitry consume a relatively large amount of power.
A need exists for a way to achieve peaking that is less costly in terms of die area, IC design complexity and power consumption.